Japanese Laid-Open Patent Publication No. 2009-289429 mentioned below discloses such a battery module. According to the disclosed technique, the voltage of each unit battery is detected in order to check the residual battery capacitance. For this purpose the positive and negative poles of each unit battery are provided with connection terminals. The connection terminals are placed on a resin board, and are further electrically connected on a relay board to be connected to a predetermined processing circuit for voltage detection.